1. Field of the Invention
The present invention relates to circuits for use as track sensor controllers for document processors. It relates further to integrated circuits of use as track sensor controllers for assuring that sensors are maintained at a level of sensitivity enabling them to detect the passage of documents with assurance while preventing false indication due to a variety of causes such as increased light transmission through holes or other flaws in the documents or due to changes in transparency of lenses caused by the accumulation of foreign matter on lenses of the sensors. The invention relates further to the provision of circuit designs of use in the production of integrated circuits to be used as track sensor controllers.
2. Description of the Prior Art
Among the known prior art devices are an "Automatic Gain Control for Photosensing Devices" described in U.S. Pat. No. 4,097,731 and 4,097,732. Those patents contain disclosures of sensors for use in apparatus where it is necessary to know when objects, such as documents, pass by a certain point and to provide a signal accordingly.
U.S. Pat. Nos. 4,097,731 and 4,097,732 relate to apparatus described therein as a beam-of-light (BOL) sensor having means for regulating the intensity of the sensor light source to compensate for extraneous factors in its operating environment, e.g., dust accumulation, component aging, misalignment, etc., that may affect consistent sensor operation. The BOL sensor includes a photosensor whose output signal is compared against a reference signal to determine if the light source intensity is of the proper level. The comparison signal is used to gate clock pulses to a counter to adjust its stored count upward or downward, dependent on whether the light source intensity is low or high, respectively. A hole filter is provided to filter out small, spurious apertures in a sensed object that would otherwise yield a double detection signal and cause an improper adjustment of the stored count.
The control apparatus disclosed in the referenced patents requires the interconnection of a number of distinct components to produce the desired results. Such as assemblage is very expensive when compared to integrated circuits produced in large quantities to provide the necessary control information. It is an object, therefore, of the present invention to provide for integrated circuits capable of operation as track sensor controllers.